2017年精河MS6.6地震前地磁异常特征分析

2017年8月9精河发生M_S6.6地震,距震中300km范围内的温泉台、克拉玛依台、乌鲁木齐台捕捉到此次地震前的地磁异常信息,本文对此进行了分析和总结,结论如下：①地磁谐波振幅比反应了观测点深部电阻率变化,2016年呼图壁M_S6.2、此次精河M_S6.6地震均发生在克拉玛依台地磁谐波振幅比异常下降之后的转折和恢复阶段;②震前83天、21天沿北天山断裂带分布的地磁台站逐日比和加卸载响应比均成组出现超限的高值,且异常高值的空间分布与震中位置有一定关联;③全国大陆地磁台站震前34天出现低点位移突变分界线,且异常集中于震中附近。     

CARE Dose 4D技术联合低kV及低剂量对比剂在MSCT头颈CTA应用

目的:探讨128层螺旋CT头颈部血管成像(CTA)应用CARE Dose 4D技术联合低剂量对比剂优化扫描方案的可行性及价值。方法:前瞻性选取接受头颈部血管成像检查的60例患者,随机分为对照组(A组)和双低剂量组(B组),每组各30例。对照组(A组)管电压120 kV,采用CARE Dose 4D技术参考管电流120 mA,对比剂用量65 mL;双低剂量组(B组)管电压80 kV,采用CARE Dose 4D技术参考管电流120 mA,对比剂用量45 mL。测量双侧颈总动脉、双侧颈内动脉及双侧大脑中动脉M1段CT值、噪声、信噪比(SNR)进行客观图像质量评价。由两名高年资主治医师采用双盲法进行图像质量评分评价。对比A组与B组间辐射剂量。结果:两名主治医师对动脉图像量质评分的一致性较高(Kappa=0.782,P<0.05)。两组动脉图像质量评分、SNR比较,差异无统计学意义(P>0.05)。双低剂量组各动脉强化CT值均高于对照组;双低剂量组容积CT剂量指数、剂量长度乘积和有效剂量均明显低于对照组;差异均具有统计学意义(P<0.05)。结论:128层MSCT头颈血管成像应用低kV及CARE Dose 4D技术联合低剂量对比剂扫描方案,不仅辐射剂量降低68%,同时造影剂用量降低30.7%,降低对比剂危害风险并节省费用,保证诊断图像质量值得临床推广。     

Direct estimation of catchment response time parameters in medium to large catchments using observed streamflow data

In single‐event deterministic design flood estimation methods, estimates of the peak discharge are based on a single and representative catchment response time parameter. In small catchments, a simplified convolution process between a single‐observed hyetograph and hydrograph is generally used to estimate time parameters such as the time to peak (T_P), time of concentration (T_C), and lag time (T_L) to reflect the “observed” catchment response time. However, such simplification is neither practical nor applicable in medium to large heterogeneous catchments, where antecedent moisture from previous rainfall events and spatially non‐uniform rainfall hyetographs can result in multi‐peaked hydrographs. In addition, the paucity of rainfall data at sub‐daily timescales further limits the reliable estimation of catchment responses using observed hyetographs and hydrographs at these catchment scales. This paper presents the development of a new and consistent approach to estimate catchment response times, expressed as the time to peak (T_Px) obtained directly from observed streamflow data. The relationships between catchment response time parameters and conceptualised triangular‐shaped hydrograph approximations and linear catchment response functions are investigated in four climatologically regions of South Africa. Flood event characteristics using primary streamflow data from 74 flow‐gauging stations were extracted and analysed to derive unique relationships between peak discharge, baseflow, direct runoff, and catchment response time in terms of T_Px. The T_Px parameters are estimated from observed streamflow data using three different methods: (a) duration of total net rise of a multipeaked hydrograph, (b) triangular‐shaped direct runoff hydrograph approximations, and (c) linear catchment response functions. The results show that for design hydrology and for the derivation of empirical equations to estimate catchment response times in ungauged catchments, the catchment T_Px should be estimated from both the use of an average catchment T_Px value computed using either Methods (a) or (b) and a linear catchment response function as used in Method (c). The use of the different methods in combination is not only practical but is also objective and has consistent results.     

Climate moderates potential shifts in streamflow from changes in pinyon‐juniper woodland cover across the western U.S.

Pinyon‐juniper (PJ) cover has increased up to 10‐fold in many parts of the western U.S. in the last 140+ years. The impacts of these changes on streamflows are unclear and may vary depending on the intra‐annual distribution and amount of precipitation. Given the importance of streamflow in the western U.S., it is important to understand how shifts in PJ woodland cover may produce changes in streamflow across the region's diverse hydroclimates. To this end, we simulated the land surface water balance with contrasting woodland and grassland cover with the Hydrologiska Byråns Vattenbalansavdelning (HBV) model at a 4‐km resolution across the distribution of PJ woodlands in the western U.S. We used shifts in evapotranspiration (ET) between woodland and grassland cover as a proxy for potential changes in streamflows. Comparison of HBV model results with paired catchment studies indicated the model reasonably simulated annual decreases in ET with changes from woodland to grassland cover. For the northern and western ecoregions of the PJ distribution in the western U.S. where precipitation predominantly occurs in the winter, HBV simulated a 25 mm (37%) annual decrease in ET with conversion to grassland from woodland. Conversely, in southern ecoregions of PJ distribution with prominent summer monsoons, annual differences in ET were only 6 mm (19%). Our results suggest that only 29% of the PJ distribution, compared to an estimated 45% based on precipitation amount alone, has the potential for meaningful increases in streamflow with land cover change from woodland to grassland.     

The impact of surface‐wave attenuation on 3‐D seismic survey design

Three‐dimensional seismic survey design should provide an acquisition geometry that enables imaging and amplitude‐versus‐offset applications of target reflectors with sufficient data quality under given economical and operational constraints. However, in land or shallow‐water environments, surface waves are often dominant in the seismic data. The effectiveness of surface‐wave separation or attenuation significantly affects the quality of the final result. Therefore, the need for surface‐wave attenuation imposes additional constraints on the acquisition geometry. Recently, we have proposed a method for surface‐wave attenuation that can better deal with aliased seismic data than classic methods such as slowness/velocity‐based filtering. Here, we investigate how surface‐wave attenuation affects the selection of survey parameters and the resulting data quality. To quantify the latter, we introduce a measure that represents the estimated signal‐to‐noise ratio between the desired subsurface signal and the surface waves that are deemed to be noise. In a case study, we applied surface‐wave attenuation and signal‐to‐noise ratio estimation to several data sets with different survey parameters. The spatial sampling intervals of the basic subset are the survey parameters that affect the performance of surface‐wave attenuation methods the most. Finer spatial sampling will reduce aliasing and make surface‐wave attenuation easier, resulting in better data quality until no further improvement is obtained. We observed this behaviour as a main trend that levels off at increasingly denser sampling. With our method, this trend curve lies at a considerably higher signal‐to‐noise ratio than with a classic filtering method. This means that we can obtain a much better data quality for given survey effort or the same data quality as with a conventional method at a lower cost.     

Fluvial to bay sequence stratigraphy and seismic facies of the Cretaceous to Paleogene successions in the MITI Sanriku‐oki well and the vicinities,the Sanriku‐oki forearc basin,northeast Japan

This paper describes the significant depositional setting information derived from well and seismic survey data for the Upper Cretaceous to Lower Eocene forearc basin sediments in the central part of the Sanriku‐oki basin, which is regarded as a key area for elucidating the plate tectonic history of the Northeast Japan Arc. According to the results of well facies analysis utilizing cores, well logs and borehole images, the major depositional environments were of braided and meandering fluvial environments with sporadically intercalated marine incursion beds. Seismic facies, reflection terminations and isopach information provide the actual spatial distributions of fluvial channel zones flowing in a north–south trending direction. The transgression and regression cycles indicate that the Upper Cretaceous to Lower Eocene successions can be divided into thirteen depositional sequences (Sequences SrCr‐0 to SrCr‐5, and SrPg‐1 to SrPg‐7). These depositional sequences demonstrate three types of stacking patterns: Types A to C, each of which shows a succession mainly comprising a meandering fluvial system, a braided fluvial system with minor meandering aspects in the upper part, and major marine incursion beds in the middle part, respectively, although all show an overall transgressive to regressive succession. The Type C marine incursion beds characteristically comprise bay center and tidal‐dominated bay margin facies. Basin‐transecting long seismic sections demonstrate a roll up structure on the trench slope break (TSB) side of the basin. These facts suggest that during the Cretaceous to Eocene periods, the studied fluvial‐dominated forearc basin was sheltered by the uplifted TSB. The selective occurrences of the Type C sequences suggest that when a longer‐scale transgression occurred, especially in Santonian and early Campanian periods, a large bay basin was developed, creating accommodation space, which induced the deposition of the Cretaceous Kuji Group along the arc‐side basin margin.     

人工智能技术气候预测应用简介

近年来,随着人工智能技术在多个领域大数据分析中的应用,许多研究工作者尝试将地学研究与人工智能跨学科结合,取得了很多新的进展,推动了地球科学的发展。其中气候预测与人类生活以及防灾减灾等息息相关,准确的气候预测至关重要。本文简要总结了人工智能技术在气候预测应用方面的研究进展,包括资料同化、模式参数化、求解偏微分方程、构建统计预测模型、改进数值模式产品释用等领域。这些研究证明了利用人工智能提高气候预测技巧的可能性和适用性,可以极大地节省计算成本和时间。然而人工智能应用也存在诸多挑战,例如数据集的构建、模型的适用性和物理可解释性等问题,对这些难点问题的研究和攻克,可以让人工智能在大数据时代中更好地补充传统地球科学方法,产生更多有益的效应,极大地改进气候预测水平。     

污泥/煤流化床混烧底灰中的重金属毒性研究

研究了污泥与煤按不同质量比例混烧后,底灰中的重金属形态分布与浸出毒性.结果表明:30:70的泥煤比使底灰中重金属硫化物及有机态和残渣态所占比例最大,即生物无效部分比例最大;在浸出毒性实验中,30:70的泥煤比使底灰重金属浸出量最小.由此推出,对环境毒害程度最小的泥煤质量比为30:70,即该实验条件下最优泥煤质量比为30:70.     

西南季风潮与2004年5月我国南方暴雨

以2004年5月初及5月中旬我国华南等地两次较大暴雨过程为例, 分析了西南季风潮与我国前汛期降水的关系。初步结论指出:西南季风潮的爆发与我国华南降水, 特别是大暴雨的形成关系极为密切, 而这次西南季风潮的爆发又与来自南半球的越赤道气流直接有关。同时指出, 这次西南季风潮的爆发主要与来自85°~95°E孟加拉湾地区所在经度的越赤道气流有关, 它们是印度洋“半球间宏观系统”的一个部分。而南海季风潮仅仅是西南季风潮的一种特例, 在这两次重大降水过程中没有南海季风潮的爆发和影响。     

2015年尼泊尔8.1级地震前后拉萨地电场观测数据变化分析

2015年4月25日尼泊尔8．1级强烈地震前后,拉萨地磁台(以下简称“拉萨台”)地电场观测数据出现了长时间、大幅度异常变化。在对拉萨台地电场观测条件、观测系统以及观测结果进行初步讨论的基础上,利用“能量合成累加”和“MSA功率谱分析”等数据处理方法,从“时间域”和“频率域”两个方面,对该异常变化的主要特征和演化过程进行了分析。结果显示,尼泊尔8.1级地震前后,拉萨台的地电场观测数据异常变化,经历了“趋势变化一扰动变化一发震期一恢复期”等发展阶段,以及“低频变化一高频变化一平稳变化高频变化”等演化过程。综合分析认为,拉萨台地电场观测异常变化特征和演化过程,与相关现象和机理研究结果基本吻合,能够完整反映强烈地震孕育、发生和发展全过程,是具有一定客观性、典型性和代表性的珍贵资料。